Electrosurface properties and acid-base equilibria of Ta2O5 and Ta2O5:Eu nanoparticles in NaCl solutions

Abstract

The electrosurface properties and aggregative stability of nanoparticles (NPs) are key factors that determine their performance and biological or environmental fate. However, there is still a lack of data on the stability of aqueous dispersions of some important NPs for biomedical applications, such as tantalum oxide. In the present work, the effects of pH, electrolyte concentration, temperature, and Eu-doping on the stability of Ta2O5 NPs aqueous dispersions were carefully studied. Surfactant-free Ta2O5 and Ta2O5:Eu NPs were synthesized via a solvothermal method. Stable hydrosols and powder samples were prepared on their basis for a comparative study. The particle size, morphology, and amorphous structure of samples were investigated by transmission electron microscopy and dynamic light scattering. The laser Doppler electrophoresis was used to investigate the pH and temperature dependence of zeta potential of NPs. Obtained results were also discussed within the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for the first time for tantalum oxide NPs. A turbidimetry study was performed to investigate the coagulation kinetics of Ta2O5 NPs in NaCl solutions. The critical coagulation concentration and stability factor were determined experimentally and via DLVO calculations; the obtained results showed a good agreement. The acid-base surface properties of samples were studied by potentiometric titration, and constants of surface acid-base equilibria were determined within 2pK-modeling.